Durability of FRP-to-concrete bonded joints subjected to 110 months accelerated laboratory and field exposure

Externally bonded fiber reinforced polymer (FRP) composites have been widely used to strengthen existing reinforced concrete (RC) structures. The predominant failure mode in FRP-strengthened RC members is debonding, which is largely dependent on the performance of the FRP-to-concrete bond interface. The durability of FRP-to-concrete bond interfaces is therefore crucial to the safety of the strengthened structure. In this study, 84 FRP-to-concrete bonded joints were tested, with different types of FRP and adhesives, including carbon FRP (CFRP) plate with Sika30, CFRP plate with Araldite106, CFRP sheet with SW -3 C, and glass FRP (GFRP) sheet with Sika330. The performance of FRP-to-concrete bond interfaces and the corresponding materials (i.e., FRP, adhesives and concrete), were tested after 8 months, 18 months, 31 months, and 110 months exposure to the wet -dry cycling environment, and 48 months and 110 months exposure to the outdoor environment. The results show that the bonded joints subjected to the wet -dry cycling environment exhibited more significant degradation compared to those subjected to the outdoor environment. In the wet -dry cycling environment, the CFRP plate with Sika 30 and CFRP sheet with SW -3 C bonded joints exhibited better durability performance with only 3% and 9% reductions in bond strength after 110 months, respectively. In contrast, the CFRP plate with Araldite106 and GFRP sheet with Sika330 bonded joints exhibited larger reductions in bond strength of 36% and 48%, respectively. Furthermore, failure mode changes were observed as the exposure time increased.